1. Field of the Invention
The invention relates generally to bit used for drilling hydrocarbon wells and, in particular aspects, the invention relates to three cone roller bits.
2. Description of the Related Art
When drilling hard and abrasive formations, the life of a drill bit is frequently limited by the wear rate of the tungsten carbide inserts and the cone steel. A shorter bit life translates directly into higher well drilling costs. When a bit become worn and loses its ability to effectively cut through formation, the entire drill string must be removed in order to replace the bit. This requires a substantial amount of time and effort.
The present invention addresses the problems associated with the prior art.
An improved bit is described as well as a method for improving the drilling life of the bit. An exemplary three cone roller bit is described having rolling cone cutters that are provided with both primary and secondary cutting elements. The primary cutting elements extend outwardly from the raised outer surfaces, or lands, of the cutter body. The secondary cutting elements are disposed within the grooves on the cutter body.
At the beginning of normal drilling operation, the primary cutting elements of the rolling cone cutters engage the borehole formation. The secondary cutting elements do not engage the formation. After substantial wear and breakage has occurred on the primary cutting elements, and wear begins to occur on the lands on the cutter body, the secondary cutting elements become active and serve as a secondary cutting structure that engages and cuts into the formation.